The present invention relates to a condenser assembly, which, in some applications, is part of an apparatus for removing liquid from a suspension.
Mixtures of liquids and solids, known as suspensions, present expensive disposal problems to the industries that generate them. Unprocessed suspensions typically cannot be disposed of in landfills due to regulations on water content. Even with more permissive regulations, it is much more expensive to transport and dispose of unprocessed suspensions as compared to solid components because transportation charges and landfill charges correspond to weight.
Additionally, the scope of potential uses of such suspensions is often substantially increased by removal of the liquid component from the solid component. Typically, the value of the dry solids arises from the decrease in weight occasioned by the removal of the liquid fraction, which leads to decreased disposal and transportation costs. The recovered dried solids may also be commercially valuable, such as if they are useable in other industrial and municipal applications (e.g., renewable fuel) or can be sold in secondary markets, such as in the case where the suspensions comprise paper, fiber, coal or mineral slurries.
Unfortunately, efforts to work around the suspension disposal problems often employ methods lacking environmental soundness. For example, many industries dump suspensions, such as waste products, into holding ponds, which are typically large concrete or plastic lined, man-made pools requiring acres of real estate. The suspensions then sit in these holding ponds while the solid materials settle at the bottom over time with the aid of only gravity. Aside from being a slow process, the potential for the pool lining to fail or result in contamination of the surrounding environment makes this a less-than-desirable solution in terms of both efficiency and environmental impact.
Industrial suspension ponds suffer from significant practical difficulties. For instance, holding ponds have a poor resulting yield (dry solid percentage content). Being passive, it also takes a long time to separate water from solids for a given volume of suspension, as compared to devices that rely on active separation. Keeping up with the output for any given suspension flow rate requires a greater area than if active separation systems are used. Two active separation systems, centrifuge processors and belt presses, each produce higher solid content yields than suspension ponds; however, they lack the ability to utilize thermodynamics to achieve 60-100% dry solid percentage yields. These active separation systems are also expensive to purchase and operate, and they are not readily scaled up or down to handle corresponding volumes of industrial suspension flow rates. The lack of portability and limitations on the amount of material which can be processed in a given time are also a significant limiting factor.
Certain drying technologies have been used to further remove water from suspensions processed by belt presses or screw presses. These drying technologies have focused on the use of thermal energy for removing water from the suspensions. For instance, drum dryers have been used; however, the technology is expensive in terms of both capital and operating costs. Belt dryers have also been used and promoted as a way of reducing footprint and costs. However, like drum dryers, belt dryers rely primarily on thermal energy to remove the water from a suspension by use of heat. Using heat to remove water requires large amounts of thermal energy to be available, which significantly adds to the operating costs of drying. In addition, both belt and drum dryers lack the ability of flexible throughputs, and also require large systems and high temperatures to operate.
In one attempt to address such limitations and disadvantages in the prior art, commonly assigned U.S. Pat. No. 9,341,410, which is incorporated herein by reference, describes an apparatus for removing liquid from a suspension. Such an apparatus comprises one or more drying chambers arranged in series. Each such drying chamber defines a substantially enclosed volume in which liquid is extracted from a suspension as it passes through the drying chamber. The apparatus further includes an internal conveyor system comprised of a conveyor belt and one or more rollers for driving the conveyor belt and transporting the suspension through the drying chambers at a substantially continuous speed. Such a conveyor belt is preferably manufactured from a material capable of withstanding the heat and pressure created within the drying chambers without significantly stretching, warping, tearing, or being otherwise rendered useless. Furthermore, the conveyor belt is preferably semi-permeable (i.e., perforated or porous), thus allowing liquids and gases to pass through the conveyor belt, while still supporting solids.
A suspension is loaded onto the conveyor belt at a first end of the conveyor belt. In each of the drying chambers, compressed and heated air is injected and applied in conjunction with a vacuum. In other words, air is pushed into and pulled from each of the drying chambers as the conveyor belt carries the suspension through the drying chambers.
With respect to the injection of air into each of the drying chambers, in some embodiments, air exits a blower and is routed via a hose to an air injection trunk line. Multiple air delivery hoses then connect the air injection trunk line to the lid of each of the drying chambers. In each drying chamber, air is then diffused by and distributed through one or more air distribution plates. The air contacts the suspension carried on the conveyor belt, and the air is then pulled through the suspension and the conveyor belt, exiting through a vacuum pipe. As a result of the application of the vacuum, the air further expands from its compressed state, through atmospheric conditions, into a negative pressure, such that the flow rate is significantly increased as the air passes through the suspension. In short, the positive-pressure injection of air into the drying chambers, combined with the vacuum pressure applied to the drying chambers, creates a pressure differential that causes rapid air expansion and increased air flow through the suspension. This facilitates efficient removal of liquid from the suspension, as there is an element of force drawing the liquid from the suspension, along with heat transfer. Thus, as the air passes through the suspension, the air becomes heavily saturated.
The heavily saturated air is then delivered to a condenser. In the condenser, the air reaches full saturation, and the liquid component (such as water) is drawn from the air as it cools and is collected in a water collection box associated with the condenser.
In some embodiments, the cooled air flows from the condenser back through the drying chambers via a series of pipes. The air is passed through the drying chambers in this manner to preheat and increase the temperature of the air. Such a preheating arrangement thus enables the use of heat that was not absorbed by the suspension to aid in the drying process.
The air is then returned to the blower. The blower again compresses and raises the temperature of the air, and the air is then again directed through the air injection trunk line to multiple air delivery hoses, and then directed into the respective drying chambers. Thus, the air is flowing through the apparatus in a closed loop (i.e., a recirculating air stream), such that the blower is also used to create the vacuum that draws air from each drying chamber.
In the present application, the focus is on the condenser (or condenser assembly) that may be used with such an apparatus for removing liquid from a suspension, or the condenser (or condenser assembly) may be used in other applications for removing a liquid component, such as water, from an air stream.